• Although viruses challenge our concept of what “living” means, they are vital members of the web of life
  • The best analogy is that of a seed that under appropriate conditions, it becomes ‘‘alive’’
  • A virus differs in that it cannot reproduce unless it is in a host cell
  • Think of the virus as the bean and the host cell as the soil
  • Viruses cannot multiply on their own, they need cellular components for their replication and protein synthetic apparatus
  • Thus, the virus is at the edge of life and can exist in two states—an inert state and a living state

For about 100 years, the scientific community has repeatedly changed its collective mind about what viruses are. First seen as poisons, then as life-forms, then biological chemicals, viruses today are thought of as being in a gray area between living and nonliving: they cannot replicate on their own but can do so in truly living cells and can also affect the behavior of their hosts profoundly.